The disclosure relates to a micromechanical sensor device with movable gate and a corresponding production method.
Although applicable to any micromechanical components, the present disclosure and the problem addressed thereby are explained on the basis of silicon-based components.
DE 44 45 553 A1 describes a semiconductor acceleration sensor comprising a semiconductor substrate, a cantilever structure, which is supported by the semiconductor substrate and has a movable electrode arranged at a predetermined distance above the semiconductor substrate, and fixed electrodes arranged on the semiconductor substrate. A sensor section is formed by the movable electrode and the fixed electrodes and detects an acceleration as a result of changes in a current between the fixed electrodes, said changes being brought about by a displacement of the movable electrode associated with the effect of the acceleration on the sensor section.
EP 0 990 911 A1 describes a micromechanical sensor based on the field effect transistor with a movable gate, which is movable in a direction parallel to the substrate surface, wherein the movement of the gate in this direction leads to an enlargement or reduction of the channel region overlapped by the gate in at least one MOSFET.
Micromechanical sensor devices with movable gate usually have evaluation circuits for detecting tiny movements, which theoretically have an excellent signal-to-noise ratio and are therefore suitable for application in e.g. extremely miniaturized acceleration sensors.
FIG. 3 shows a schematic cross-sectional view for elucidating a known micromechanical sensor device with movable gate in vertical cross section.
In FIG. 3, reference sign 2 denotes a silicon substrate, in which a drain region 3, a source region 4 and therebetween a channel region 7 of a field effect transistor are provided. A gate insulation layer 5, for example an oxide layer, is provided on the channel region 7. Surface charges on the insulation layer 5 are indicated by reference sign 6. A movable gate electrode 1 is arranged movably above the substrate 2 in a manner separated by an interspace Z.
A particular feature of a sensor device constructed in this way is the increased noise for deflections in the x,y-direction which is observed in real applications. This increased noise can largely be attributed to parasitic leakage currents.